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<title>5.8.1 Scheduler Objects </title>
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<h2><a name="SECTION007810000000000000000"></a><a name="scheduler-objects"></a>
<br>
5.8.1 Scheduler Objects 
</h2>

<p>
<tt class="class">scheduler</tt> instances have the following methods:

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-792' xml:id='l2h-792' class="method">enterabs</tt></b>(</nobr></td>
  <td><var>time, priority, action, argument</var>)</td></tr></table></dt>
<dd>
Schedule a new event. The <var>time</var> argument should be a numeric type
compatible with the return value of the <var>timefunc</var> function passed 
to the constructor. Events scheduled for
the same <var>time</var> will be executed in the order of their
<var>priority</var>.

<p>
Executing the event means executing
<code><var>action</var>(*<var>argument</var>)</code>.  <var>argument</var> must be a
sequence holding the parameters for <var>action</var>.

<p>
Return value is an event which may be used for later cancellation of
the event (see <tt class="method">cancel()</tt>).
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-793' xml:id='l2h-793' class="method">enter</tt></b>(</nobr></td>
  <td><var>delay, priority, action, argument</var>)</td></tr></table></dt>
<dd>
Schedule an event for <var>delay</var> more time units. Other then the
relative time, the other arguments, the effect and the return value
are the same as those for <tt class="method">enterabs()</tt>.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-794' xml:id='l2h-794' class="method">cancel</tt></b>(</nobr></td>
  <td><var>event</var>)</td></tr></table></dt>
<dd>
Remove the event from the queue. If <var>event</var> is not an event
currently in the queue, this method will raise a
<tt class="exception">RuntimeError</tt>.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-795' xml:id='l2h-795' class="method">empty</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Return true if the event queue is empty.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-796' xml:id='l2h-796' class="method">run</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Run all scheduled events. This function will wait 
(using the <tt class="function">delayfunc</tt> function passed to the constructor)
for the next event, then execute it and so on until there are no more
scheduled events.

<p>
Either <var>action</var> or <var>delayfunc</var> can raise an exception.  In
either case, the scheduler will maintain a consistent state and
propagate the exception.  If an exception is raised by <var>action</var>,
the event will not be attempted in future calls to <tt class="method">run()</tt>.

<p>
If a sequence of events takes longer to run than the time available
before the next event, the scheduler will simply fall behind.  No
events will be dropped; the calling code is responsible for canceling 
events which are no longer pertinent.
</dl>

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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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